Original articles

Distribution of void fraction in bubbly flow through a horizontal channel： Bubbly boundary layer flow, 2nd report

　

YUKI YOSHIDA¹, YOSHIAKI TAKAHASHI¹, HIROHARU KATO², and MADAN MOHAN GUIN³

　

¹ Technology Development Department, IShikawajima-Harima Heavy Industries co.,Ltd., 2-1-1 Toyosu, Koto-ku, Tokyo 135-0061, Japan

²Department of Naval Architecture and ocean Engineering, UniVersity ot Tokyo, 7-3-1 Hongo, Bunkyo-ku Tokyo 113, Japan

³I.L・E・M Co., Ltd., 2-1-1 Toyosu, Koto-ku, Tokyo 135, Japan

　

Abstractt： A method of enveloping the hull with a sheet of microbubbles is discussed. It forms part of a study on means of reducing the skin friction acting on a ship's hull. In this report, a bubble traveling through a horizontal channel is regarded as a diffusive particle. Based on this assumption, an equation based on flow flux balance is derived for determining the void fraction in approximation. The equation thus derived is used for calculation, and the calculation results are compared with reported experimental data. The equation is further manipulated to make it compatible with a mixing length model that takes into account the presence of bubbles in the liquid stream. Among the factors contained in the equation thus derived, those affected by the presence of bubbles are the change of mixing length and the difference in the ratio of skin friction between cases with and without bubbles. These factors can be calculated using the mean void fraction in the boundary layer determined by the rate of air supply into the flow field. It is suggested that the ratio between boundary layer thickness and bubble diameter could constitute a significant parameter to replace the scale effect in estimating values applicable to actual ships from corresponding data obtained in model experiments.

　

Key words： bubbly flow, turbulent boundary layer, mixing length, skin friction, void fraction

　

Address correspondence to： Y. Yoshida

Received for publication on June 30, 1997; accepted on Sept. 30, 1997

　

List of symbols

　

Suffixes

G gas

L liquid

O absence of bubbles

BACK　　　CONTENTS　　　NEXT